Mantaflow fluid does not take the shape of a sphere (Blender 2.8)
The container/domain will always use the bounding box of the object (the cube/rectangle that enclose the object), you can see it by changing the object display to Bounds:



If you want to have the liquid stay in a shape that's not a rectangular box, you have to use a separate object set to Effector to act as a container.

For example, if you want the sphere to act as the walls of a container:


Duplicate it
Set the fluid type to Effector
Go into edit mode, and flip the normals so that they face inwards.
Back inside the simulation settings, set Is Planar, and turn up the Surface Thickness until things stop leaking





Put your flow source inside the sphere.
Bake
???
Profit!


You should get something looking like this: 



Here's the blend file: